Pour heavy cream into a large bowl + add in the yogurt, stir to combine
Cover with a dish towel and let it sit at room temperature for about 48 hours (will thicken as it sits)
Pour the mixture into a stand mixer + whisk on medium until you have butter - first you'll have whipped cream, then the butter will separate from the buttermilk
Strain the buttermilk into a bowl (save it if you want!), then put the butter into a bowl of ice water
Squeeze out excess buttermilk
Empty the bowl, then do another round of the ice water + squeeze again until water is clear
Add sea salt, to taste + mix well
Form into a ball, wrap in parchment paper or place in an airtight container + store in the fridge